This invention relates generally to the formation of designs in the smooth surface of a hard substrate, and more particularly to a method and apparatus used in the method to create such designs by acid etching or sand or grit blasting processes to create such designs.
The surfaces of hard material substrates, such as glass, plastic, ceramics, and marble, granite, or other stone, are often decorated with a design that is placed in the surface in relief. A portion of the surface is removed to a desired depth to create a contrast between the preexisting surface and that portion of the surface which has been removed. For glass surfaces, for example, a portion of the surface may be removed by acid etching or sandblasting. Designs in granite or marble surfaces are typically made by impacting the surface with small particles of aluminum oxide, steel shot, garnet, sand, or glass beads, a process which will hereinafter be generically referred to as sandblasting. For example, designs are placed on tombstones by this process.
Sandblasting may also be used to place designs in metals such as aluminum, brass, bronze and copper. Wood can also be sandblasted. However, the surface must first be sprayed or brushed with a clear acrylic or other sealer type paint. This gives the wood a smooth hard surface and prevents moisture from getting into the wood.
In either the acid etching or sandblasting processes, a protective mask in the shape of the desired design is applied to a portion of the surface of the substrate on which the design is to be made. The mask protects the covered portion of the surface of the substrate from the acid etchant in the case of acid etching or from the erosive particles in the case of sandblasting. That is, the surface area under the mask remains, while the acid etchant or erosive particles attack those areas of the surface unprotected by the mask, thereby removing the unprotected areas of the surface to a desired depth. The depth of removal can be varied somewhat by varying the amount of time the substrate surface is exposed to the acid etchant or erosive particles.
Current methods of acid etching or sandblasting, however, are highly labor intensive, require artistic skill, and are time consuming.
In conventional glass etching techniques, a silk screen stencil is first made and then applied to the glass surface. The silk screen has permeable and impermeable areas corresponding to the design to be placed on the surface. An acid etchant is applied to the silk screen and attacks the glass surface through the permeable areas of the silk screen. This process is explained in U.S. Pat. No. 4,436,776 to Wojcik. In addition to silk screens, stencils to etch glass have been made of plastic foil as in U.S. Pat. No. 4,316,766 to Levin et al. U.S. Pat. No. 3,769,113 to Gruenke, Jr., discloses the application of an acid resistant material, such as wax, to the glass surface to be etched.
Another technique used to decoratively etch glass uses a screenable, organic-based acid resist. The process is commonly called silk screening, but the screen materials are usually nylon, polyester, or stainless steel. The resist is heated to a liquid state and applied by screening to form a decorative pattern on the glass surface. The mask material is required to solidify over a period of time after contacting the glass. The glass article is then immersed in an acid bath. All surfaces of the glass article not covered with the resist are etched by the acid.
After the etching process is complete, the glass is rinsed with water and the mask material must then be removed. This may be done by soaking the glass in a hot solvent to soften the mask material and then washing with detergent to remove the material. Alternatively, the glass may be heated to a temperature for a period of time to burn off the mask material.
Glass, granite, marble, and other hard surfaces are commonly etched by sandblasting through a stencil having the decorative design. The stencil is usually made of a resilient material such as rubber or plasticized vinyl. The areas of the article which are to remain unetched are covered with the stencil. This method is generally disclosed in U.S. Pat. No. 1,840,226 to Chase, U.S. Pat. No. 3,687,750 to Jamieson, U.S. Pat. No. 3,515,528 to Luther et al., and U.S. Pat. No. 1,676,637 to Di Bona et al. These procedures have the inherent shortcoming of requiring the making of a separate stencil before the design can be produced in the glass or other surface.
More recently, it has been proposed to apply a liquid photosensitive resin directly to the surface to be etched by either acid etching or sandblasting. U.S. Pat. No. 4,451,329 to Batchelor et al., discloses application of an ultraviolet curable combination of acrylic oligomers, cross-linkable comonomers, and photosensitizing agents, which is rendered etchant-resistent upon cross-linking by exposure to ultraviolet radiation. The mask material is applied using existing techniques, such as screening, brushing, or spraying. Alternatively, the mask may be applied by a pad transfer technique. Either method has disadvantages. Applying a uniform thickness of liquid mask is difficult. The pad transfer technique requires the step of transferring the mask from a pad to the article which is to be etched.
U.S. Pat. No. 4,430,416 discloses use of a transfer element having a photosensitive resin for a sandblasting process. U.S. Pat. No. 4,321,105 discloses another transfer element for embossing designs by acid etching. Again, both of these techniques require transferring steps.
In view of the shortcomings of the existing methods for acid etching and sandblasting decorative designs into smooth, hard substrates, there is a need for a simpler, more economic, and faster technique for applying a mask in the desired decorative configuration to the surface of the substrate.